US8310995B2 - Systems and methods for wireless communication using SDMA - Google Patents

Systems and methods for wireless communication using SDMA Download PDF

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US8310995B2
US8310995B2 US11/797,321 US79732107A US8310995B2 US 8310995 B2 US8310995 B2 US 8310995B2 US 79732107 A US79732107 A US 79732107A US 8310995 B2 US8310995 B2 US 8310995B2
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sdma
stations
station
channel
wireless
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US20070274256A1 (en
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Shinji Murai
Tomoaki Ishifuji
Takashi Yano
Masaaki Shida
Shigenori Hayase
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Hitachi Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W28/00—Network traffic management; Network resource management
    • H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
    • H04W28/18—Negotiating wireless communication parameters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/046—Wireless resource allocation based on the type of the allocated resource the resource being in the space domain, e.g. beams

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  • the present invention relates to systems, methods, and apparatuses for wireless communication to communicate with a plurality of terminals or stations using Space Division Multiple Access (SDMA) with one and the same frequency at one and the same point of time, and in particular, to systems, methods, and apparatuses for wireless communication in which resources of space and time are efficiently allocated in consideration of Quality of Service (QoS).
  • SDMA Space Division Multiple Access
  • AAA Adaptive Array Antenna
  • MIMO Multiple Input Multiple Output
  • these techniques when viewed from another perspective, can be categorized into (1) Space Division Multiple Access (SDMA) to transmit signals to two or more stations and (2) Space Division Multiplexing (SDM) to transmit signals to one and the same station.
  • SDMA Space Division Multiple Access
  • SDM Space Division Multiplexing
  • the amplitude and phases of signals communicated respectively via a plurality of antennas are adjusted using weights to transmit mutually different data sequences to a plurality of stations with one and the same frequency at one and the same point of time by use of the spatial orthogonality of the signals on the transmission paths.
  • the amplitude and phases of signals communicated respectively via a plurality of antennas are adjusted using weights to transmit mutually different data sequences to one and the same station with one and the same frequency at one and the same point of time by use of the spatial orthogonality of the signals on the transmission paths.
  • MIMO-SDMA implemented as a combination of the SDMA and MIMO techniques.
  • the SDMA technique is employed for different terminals and the SDM technique is utilized for the one and the same terminal.
  • the SDMA technique is described, for example, in an article, T. Ohgane, “A Study on a channel allocation scheme with an adaptive array in SDMA” IEEE 47th VTC, Vol.
  • the SDM technique is described, for example, in an article, G. J. Foschini, “Layered space-time architecture for wireless communication in fading environment when using multi-element antennas”, Bell Labs Tech. J. Autumn 1996, pp. 41-59.
  • the MIMO-SDMA technique is described, for example, in an article, Andre Bourdoux, Nadia Khaled, “Joint Tx-Rx Optimisation for MIMO-SDMA Based on a Null-space Constraint”, IEEE2002. pp. 171-172.
  • These applications have requirements of communication quality such as transmission bands and allowable transmission delay associated with communications thereof.
  • Various schemes have already been discussed to guarantee such requirements for the application services.
  • the communication quality of the station is individually evaluated to secure the required communication quality.
  • a time-division-based QoS control method of, for example, Enhanced Distributed Channel Access (EDCA) defined by IEEE80211e time is allocated with a higher priority level to a station requiring high communication quality.
  • EDCA Enhanced Distributed Channel Access
  • an access point communicates with a plurality of stations with the same frequency at the same point of time using the SDMA, it is known that there exist a plurality of combinations (to be referred to as SDMA groups hereinbelow) of stations and the transmission quality of each station varies depending on the SDMA group associated with the station.
  • a wireless communication apparatus including a first evaluation unit which designates particular stations as an SDMA group to evaluate each of the stations of the SDMA group and a first decision unit which determines stations for the SDMA and time allocation for each SDMA group, wherein the first decision unit allocates wireless resources using the first evaluation unit.
  • the apparatus further includes a second evaluation unit to evaluate a performance required by each station and a performance required by each application. The first decision unit allocates wireless resources using the first and second evaluation units.
  • the first decision unit allocates wireless resources capable of optimization to be carried out by using a calculation method of maximizing the overall channel capacity, a calculation method of equally distributing the channel capacity to the respective stations, a calculation method corresponding to a system including uplink and downlink transmission, a calculation method corresponding to a system implemented in consideration of the quality of service, and a calculation method corresponding to a system including data of absolute guarantee type and data of relative guarantee type.
  • the present invention there are selected a plurality of SDMA group candidates to be used in a period of time in which the wireless resources are allocated and a period of time is allocated to each of the selected SDMA groups, to thereby improve the wireless resource utilization efficiency and the communication stability. Also, while securing the channel capacity for the stations for the data of absolute guarantee type, the remaining wireless resources can be distributed to the stations for the data of relative guarantee type and hence the channel capacity can be expectedly increased.
  • FIG. 1 is a diagram showing an outline of a wireless communication system according to an embodiment of the present invention.
  • FIG. 2 is a block diagram showing a configuration of an access point (AP) 101 .
  • FIG. 3 is a diagram showing a RF unit of FIG. 2 .
  • FIG. 4 is a diagram showing a signal processing unit of FIG. 2 .
  • FIG. 5 is a diagram showing a packet controller of FIG. 2 .
  • FIG. 6 is a diagram showing a wireless resource allocator of FIG. 2 .
  • FIG. 7 is a flowchart showing operation to allocate wireless resources.
  • FIG. 8 is a diagram showing an example of a table created in step 302 of FIG. 7 (No. 1).
  • FIG. 9 is a diagram showing an example of a table created in step 302 of FIG. 7 (No. 2).
  • FIG. 10 is a diagram showing an example of a table created in step 302 of FIG. 7 (No. 3).
  • FIG. 11 is a diagram showing an example of a table created in step 303 of FIG. 7 (No. 1).
  • FIG. 12 is a diagram showing an example of a table created in step 303 of FIG. 7 (No. 2).
  • FIG. 13 is a graph showing an example of wireless resource allocation according to the present invention.
  • FIG. 14 is a graph comparing communication characteristics between the conventional method and the method of the present invention (No. 1).
  • FIG. 15 is a graph comparing communication characteristics between the conventional method and the method of the present invention (No. 2).
  • FIG. 1 shows an outline of a wireless communication system according to an embodiment of the present invention.
  • an access point (AP) 101 indicates a base station which includes a plurality of antennas and which is capable of adaptively changing directivity of the antennas.
  • the access point 101 may be connected to a wired network 102 .
  • Each of stations (STAs) 103 - 1 to 103 -N includes at least one antenna. If a plurality of antennas are disposed, the station 103 changes directivity of the antennas.
  • FIG. 2 shows a configuration of the access point 101 in a block diagram.
  • the access point 101 includes a plurality of antennas 201 to conduct wireless communication with stations, a RF (radio frequency) unit 202 , a signal processing unit 203 , a modem controller 204 , and a packet controller 205 which are connected to each other in this order.
  • the access point 101 further includes, as an aspect of the present invention, a wireless resource allocator 206 to obtain channel state information and require information to conduct allocation of wireless resources.
  • FIG. 3 shows a configuration of the RF unit 202 in a block diagram.
  • the wireless unit 202 includes first to m-th wireless modules 202 - 1 to 202 - m .
  • Each wireless module includes a transmitter 202 - a , a receiver 202 - b , and a switch 202 - c .
  • the switch 202 - c conducts a changeover operation between the transmitter 202 - a and the receiver 202 - b to carry out the uplink transmission and the downlink transmission in a time-division fashion.
  • the transmitter 202 - a includes an up-converter and a power amplifier and converts a signal 10 - 1 to 10 - m inputted from the signal processing unit 203 from a low-frequency signal into a high-frequency signal (carrier) and amplifies the high-frequency signal to output the amplified signal to the antenna 201 .
  • the receiver 202 - b of the RF unit 202 includes a power amplifier and a down-converter and converts a signal received by the antenna 201 from a high-frequency signal into a low-frequency signal and amplifies the low-frequency signal to output the amplified signal 10 to the signal processing unit 203 . Description will be given in detail of a signal 5 later together with the wireless resource allocator 206 .
  • FIG. 4 shows a configuration of the signal processing unit 203 in a block diagram.
  • the signal processing unit 203 includes a combining module 203 - a , a weight module 203 - b , and a channel state information calculating module 203 - c . It is assumed in this situation that the weight module 203 - b includes at most m by m weight values.
  • the signal processing unit 203 receives signals 10 - 1 to 10 - m from the RF unit 202 and separates and extracts therefrom signals 20 - 1 to 20 - m to output the signals 20 - 1 to 20 - m to the modem controller 204 .
  • the combining module 203 - a multiplies the input signals 10 - 1 to 10 - m respectively by weights 203 - b which are calculated by the wireless resource allocator 206 and which are required for reception signals to obtain signals 20 - 1 to 20 - m and then outputs the signals 20 - 1 to 20 - m to the modem controller 204 .
  • the signal processing unit 203 receives the signals 20 - 1 to 20 - m from the modem controller 204 to conduct combining operation for the signals and outputs the combined signals 10 - 1 to 10 - m to the RF unit 202 .
  • the combining module 203 - a multiplies the input signals 20 - 1 to 20 - m respectively by weights 203 - b which are calculated by the wireless resource allocator 206 and which are required for transmission signals to obtain signals 20 - 1 to 20 - m and then outputs the signals 20 - 1 to 20 - m to the RF unit 202 .
  • the channel state information calculating module 203 - c extracts information of states of channels between the access point and the respective stations.
  • the calculating module 203 - c is arranged in the signal processing unit 203 in the embodiment, the module 203 - c may also be installed in, for example, the RF unit 202 .
  • the signal processing unit 203 may additionally includes signal processing functions, for example, the Fast Fourier Transform (FFT) function and/or the Inverse FFT (IFFT) function necessary for the processing such as Orthogonal Frequency Division Multiplexing (OFDM).
  • FFT Fast Fourier Transform
  • IFFT Inverse FFT
  • OFDM Orthogonal Frequency Division Multiplexing
  • the modem controller 204 executes processing for modulation and demodulation.
  • modulation processing the modem controller 204 modulates signals 30 - 1 to 30 - m inputted from the packet controller 205 and outputs the resultant signals 20 - 1 to 20 - m to the signal processing unit 203 .
  • demodulation processing the modem controller 204 demodulates signals 20 - 1 to 20 - m inputted from signal processing unit 203 and outputs the resultant signals 30 - 1 to 30 - m to the packet controller 205 . Description will be given in detail of a signal 25 later together with the wireless resource allocator 206 .
  • FIG. 5 shows the configuration of the packet controller 205 in a block diagram.
  • the packet controller 205 includes an interface controller 205 - a and a buffer controller 205 - b .
  • the interface controller 205 - a includes an interface for the wired network 102 and an interface for applications in the access point and executes processing for transmission and reception of information signals and control signals to be handled in the communication system.
  • the interface controller 205 executes, for example, predetermined processing which conforms to IEEE80211 such as processing to convert a PHYsical layer (PHY) frame and a Media Access Control (MAC) frame and processing to extract information signals and control signals from an MAC frame.
  • PHY PHYsical layer
  • MAC Media Access Control
  • the buffer controller 205 - b conducts a control operation to implement the wireless resource allocation calculated by the wireless resource allocator 206 .
  • the buffer controller 205 - b includes a buffer module to store information therein and a selector to select data of the buffer module.
  • Information necessary for the wireless resource allocation such as capacity of a buffer in the buffer controller 205 - b may be outputted from the information 60 to the wireless resource allocator 206 .
  • Signals 40 to be communicated with the wired network 102 include N signals the number of which is equal to that of the stations. However, the number of signals 40 is not restricted by the configuration of the embodiment. A signal 35 will be described in detail later together with the wireless resource allocator 206 .
  • FIG. 6 shows a configuration of the wireless resource allocator 206 in a block diagram.
  • the allocator 206 includes a channel state information evaluator 206 - a , a require information evaluator 206 - b , an optimizer 206 - c , a scheduler 206 - d , a transmit-receive controller 206 - e , a weight calculator 206 - f , a modem controller 206 - g , and a buffer controller 206 - h .
  • the allocator 206 conducts a control operation for the wireless unit 202 , the signal processing unit 203 , the modem controller 204 , and the packet controller 205 according to a result of wireless resource allocation.
  • the channel state information evaluator 206 - a receives channel state information 50 extracted by the channel state information calculator 203 - c for a plurality of stations and accordingly calculates communication performance, for example, the channel capacity for the stations of each SDMA group.
  • the require information evaluator 206 - b receives require information 60 extracted by the interface controller 205 - a to calculate communication performance required by each station or application.
  • the optimizer 206 - c selects, according to signals produced from the evaluators 206 - a and 206 - b , candidates of a plurality of SDMA groups to be used within a period of time for the wireless resource allocation and then calculates a ratio of time for each SDMA group thus selected.
  • the optimizer 206 - c outputs the selected SDMA groups and the ratios of time for the SDMA groups to the scheduler 206 - d .
  • the scheduler 206 - d conducts a scheduling operation on the basis of the calculation result from the optimizer 206 - c .
  • the scheduler 206 - d conducts the scheduling under a condition that the total of the periods of time to be used by the respective SDMA groups corresponds to the ratios of time calculated by the optimizer 206 .
  • the transmit-receive controller 206 - e outputs to the wireless unit 202 signal 5 for a changeover between transmission and reception in an order scheduled by the scheduler 206 - d .
  • the weight calculator 206 - f calculates transmission and reception weights for the SDMA by use of the signal 50 from the channel state information calculator 203 - c .
  • the weight calculator 206 - f outputs weight signals 15 to the signal processing unit 203 in a sequence scheduled by the scheduler 206 - d .
  • the modem controller 206 - g generates a control signal 25 for which the modulation multiple number and the coding ratio are determined by using the signal 50 from the channel state information calculator 203 - c and outputs the signal 25 to the modem controller 204 in the order scheduled by the scheduler 206 - d .
  • the buffer controller 206 - h outputs to the packet controller 205 a control signal 35 to extract a packet scheduled by the scheduler 206 - d.
  • N indicates the number of stations and m is the number of antennas connected to the access point 101 .
  • the RF unit 202 , the signal processing unit 203 , the modem controller 204 , and the packet controller 205 each include constituent components corresponding to the number of antennas (m) and the number of stations (M). However, it is not necessarily required to use all of the constituent components.
  • the transmission system and the reception system are commonly configured for the antenna 201 , the RF unit 202 , the signal processing unit 203 , the modem controller 204 , and the packet controller 205 , the transmission system and the reception system may also be separated from each other.
  • FIG. 7 is a flowchart showing a processing procedure of the wireless resource allocation according to an embodiment of the present invention. Description will now be given of a procedure in which information items regarding channels and requirements are extracted, the information items are converted according to one and the same index, for example, channel capacity, and then the ratio of time is optimized for each SDMA on the basis of the information items.
  • step 301 information of a wireless channel between the access point and each station is extracted.
  • the processing is executed by the channel state information calculator 203 - c .
  • the information of the wireless channel is measured in a predetermined method.
  • the access point measures the information.
  • the station measures the information.
  • the information thus measured is on a wireless channel in a direction from the station to the access point.
  • the information thus measured is on a wireless channel in a direction from the access point to the station and the result measured by the station is notified to the access point.
  • a channel matrix (representing channel responses corresponding to the number of the antennas) is extracted in the second method.
  • a reception signal R k [r 1,k , r 2,k , . . . , r n,k ] T received by a station STA #k
  • R k H k T k
  • T k [t 1,k , t 2,k , . . . , t n,k ] T from the access point to the station STA #k
  • R k H k T k
  • Station (STA) #k detects the channel matrix Hk by use of a detection algorithm, for example, Zero Forcing (ZF) as below.
  • H k R k T k ⁇ 1 (2)
  • the arithmetic operation may be carried out using an averaging operation in which the pilot signals received a plurality of times are averaged. In this case, if the fluctuation rate of the channel is sufficiently low, it is possible to reduce the influence from noise, and hence the estimation precision to estimate the channel state can be increased.
  • the channel state information in step S 301 includes, in addition to the Signal to Noise power Ratio (SNR), the Signal to Interference power Ratio (SIR), and the Received Signal Strength Indicator (RSSI); channel parameters such as the Bit Error Rate (BER), a delay profile, a modulation multiple number, a coding ratio, and/or the diffusion ratio.
  • SNR Signal to Noise power Ratio
  • SIR Signal to Interference power Ratio
  • RSSI Received Signal Strength Indicator
  • channel parameters such as the Bit Error Rate (BER), a delay profile, a modulation multiple number, a coding ratio, and/or the diffusion ratio.
  • BER Bit Error Rate
  • weights are calculated using as reference signals a central frequency, an incoming direction, a modulation method, and polarization of a desired radio wave, which are preliminary knowledge to construct an evaluation function.
  • the evaluation function is calculated also using channel state information.
  • step S 302 the SDMA groups to be used in the wireless resource allocation are listed in step S 302 .
  • the SDMA technique there exist a plurality of combinations for the SDMA groups. Channel quality is periodically calculated for the combinations.
  • FIG. 8 shows the channel capacity of SDMA groups in addition to the SDMA group candidates. The channel capacity is calculated in step S 304 .
  • the SDMA group candidates are expanded. This is carried out by the channel state information evaluator 206 - a . If the MIMO-SDMA technique is employed, the number of streams can be changed by changing transmission and reception weights in the signal processing unit 203 . Description will now be given of operation of MIMO-SDMA in a system including, for example, an access point with four antennas, a station STA # 1 with two antennas, a station STA # 2 with two antennas, and a station STA # 3 with two antennas. In this system, the number of streams is limited to the number of antennas of the access point, i.e., four.
  • FIG. 9 shows the channel capacity of SDMA groups in addition to the SDMA group candidates. The channel capacity is calculated in step S 304 .
  • step S 302 the system provides a power distribution method for each SDMA.
  • This processing is executed by the channel state information evaluator 206 - a .
  • WF Water Filling
  • FIG. 10 shows the number of simultaneous connections in a system including, for example, an access point with four antennas, a station STA # 1 with two antennas, a station STA # 2 with two antennas, and a station STA # 3 with two antennas.
  • the number of simultaneous connections is at most two.
  • the patterns of combinations are expanded as indicated by candidates 1 and 2 .
  • FIG. 10 shows the channel capacity of SDMA groups in addition to the SDMA group candidates. The channel capacity is calculated in step S 304 .
  • step S 303 to reduce the number of calculation steps, the system selects SDMA group candidates to be used in the wireless resource allocation.
  • the processing is executed by the channel resource allocator 206 (specifically, the channel state information evaluator 206 - a ). Since it is possible to use all of the SDMA groups listed in step S 302 , step S 303 may be dispensed with.
  • step S 303 an index value representing a correlation between channels is calculated using the channel state information extracted, for example, in step S 301 .
  • the processing is executed by the wireless resource allocator 206 (specifically, the channel state information evaluator 206 - a ).
  • the system calculates, for example, a correlation value between two antennas. That is, the system calculates a vector product between a channel matrix generated from a first antenna and a result of conjugate transposition of a channel matrix generated from a second antenna. From the product, an absolute value of each channel matrix is subtracted.
  • the correlation value ⁇ TX1TX2 between the channel matrix formed by an antenna Tx 1 and that formed by an antenna Tx 2 is expressed as follows.
  • ⁇ T ⁇ 1 ⁇ T ⁇ 2 h T ⁇ 1 H ⁇ h T ⁇ 2 ⁇ h T ⁇ 1 ⁇ ⁇ ⁇ h T ⁇ 2 ⁇ ( 3 )
  • the correlation value is calculated in this way.
  • the system may calculates a combination of channel characteristics formed by the antennas. Or, it is also possible to select an appropriate number of antennas for the calculation of the channel characteristics.
  • the total of the correlation values is calculated using expression (3) to select a combination for which the total is less than a threshold value (a combination with a lower correlation).
  • the combination is designated as an SDMA group candidate. Any combination other than the combination for which the total exceeds a threshold value (a combination with a higher correlation) is selected.
  • 11 shows an example in which the total of correlation values is calculated for each station in a system including, for example, an access point with four antennas, a station STA # 1 with two antennas, a station STA # 2 with two antennas, and a station STA # 3 with two antennas. If the number of simultaneous connections is two, the correlation value for a combination of STA # 1 and STA # 3 is 0.9. For a high correlation, it is not likely to obtain large channel capacity. Therefore, the SDMA group including STA # 1 and STA # 3 is removed from the candidates. This resultantly reduces the number of calculation steps.
  • a second mode of step S 303 the system employs a method in which SDMA groups are beforehand estimated to reduce the number of calculation steps.
  • the processing is executed by the wireless resource allocator 206 (specifically, the channel state information evaluator 206 - a ).
  • the wireless resource allocator 206 specifically, the channel state information evaluator 206 - a .
  • the system estimates a direction of each station, not the correlation. Stations apart from each other are categorized to belong to one and the same SDMA group.
  • an access point with four antennas, a station STA # 1 with two antennas, a station STA # 2 with two antennas, and a station STA # 3 with two antennas.
  • an MUSIC algorithm a method of analyzing an eigen value of a covariance matrix of data received by a plurality of antennas
  • a method of detecting the direction by turning 360° a beam having sharp directivity By using such method of estimating the incoming direction, the system generates a table as shown in FIG. 12 . It is not likely for stations, which exist in the vicinity of each other with respect to the direction, to gain large channel capacity.
  • the system employs a method to beforehand estimate SDMA groups to thereby reduce the number of calculation steps.
  • the processing is executed by the wireless resource allocator 206 (specifically, the channel state information evaluator 206 - a ).
  • the channel capacity per station is larger in the communication conducted between a first unit and a second unit using the SDM technique in a one-to-one communication without using the SDMA technique than that in the communication conducted between a first unit and a plurality of units in a one-to-multi communication using the SDMA technique. Therefore, for each station, the system first confirms the channel state using, for example, the Received Signal Strength Indicator (RSSI). If the state is not appropriate, the calculation for the situation of the SDMA technique is not conducted for the station. The amount of calculation steps is resultantly reduced.
  • RSSI Received Signal Strength Indicator
  • the system calculates the channel capacity of the station when the SDMA technique is employed.
  • the processing is executed by the wireless resource allocator 206 (specifically, the channel state information evaluator 206 - a ). Description will now be given of an example in which the MIMO-SDMA technique is employed for an access point with four antennas, a station STA # 1 with two antennas, and a station STA # 2 with two antennas.
  • a reception signal R 1 of STA # 1 and a reception signal R 2 of STA # 2 are represented, using a transmission signal T 1 to STA # 1 , a transmission signal T 2 to STA # 2 , and channel matrices between the access point and the stations H 11 , H 12 , H 21 , and H 22 as follows.
  • E-SDM Eigenbeam Space Division Multiplex
  • the channel capacity is obtained for each station when the MIMO-SDMA technique is employed.
  • the above method is available to obtain the channel capacity, it is also possible to estimate the channel capacity as a value estimated by approximation.
  • the evaluation of the channel state information namely, the calculation of the channel capacity and calculation of weights are carried out by the channel state information evaluator 206 - a .
  • the weight calculator 206 - f as shown in FIG. 6 .
  • V and U are inputted via the weight signal 15 to the weight module 203 - b to be multiplied by each other in the combining module 203 - a .
  • the processing is executed in an order of steps S 302 , S 303 , and S 304 , namely, the listing, selection, and calculation of SDMA groups.
  • the processing may also be executed in an order of steps S 302 , S 304 , and S 303 .
  • step S 305 the system extracts information of requirement from each station or application.
  • This processing is executed by the interface controller 205 - a .
  • the require information is measured in a predetermined method.
  • the require information is extracted by use of a predetermined protocol such as Hybrid Coordination Function Controlled Channel Access (HCCA) prescribed in the standard of IEEE802.1.1e.
  • HCCA Hybrid Coordination Function Controlled Channel Access
  • it is determined to conduct, before communication is started between a station and an access point, negotiation of communication quality therebetween.
  • the system measures information regarding a requirement described in a packet transmitted to the system. For example, the system extracts require information by analyzing a User's Priority header of IEEE802.1D.
  • the require information in step S 305 includes, throughput, priority, an application type, capacity of a buffer, delay, and jitter, in addition to the channel capacity.
  • step S 306 the require information extracted in step S 305 is converted into the index equal to that of the information processed in step S 304 .
  • the processing is executed in the require information evaluator 206 - b .
  • the information of the wireless channel is converted into, for example, the channel capacity. If only the SNR is notified as the require information, the information is converted into the channel capacity by use of expression (6).
  • the resultant value corresponds to a signal inputted from the require information evaluator 206 - b to the optimizer 206 - c . If the require information is associated with higher priority or a long delay, a large value may be outputted to the optimizer 206 - c.
  • the index value obtained by evaluating the channel state information or the require information is represented by a positive number. It is assumed that the larger the value is, the better the state of the channel is or the stronger the requirement is. However, there may be employed other indices. Also to reduce the amount of feedback information, it is possible to share, among the access point and the stations, tables each of which includes the information obtained by evaluating the channel state information and the channels such that table numbers respectively assigned thereto are communicated therebetween.
  • step S 307 according to the channel state information and the require information, a plurality of SDMA group candidates are selected to calculate the time ratios for the selected SDMA groups.
  • the processing receives as inputs thereto the SDMA groups and the tables ( FIGS. 8 to 10 ) regarding the channel capacity for each station which are obtained by the channel state information evaluator 206 - a , i.e., through processing in steps 302 and S 303 and the channel capacity obtained in step S 306 by the require information evaluator 206 - b .
  • the processing determines the SDMA groups to be used and calculates the time ratio for each of the SDMA groups.
  • the linear programming is a method of obtaining a maximum or minimum value of an objective function under conditions of constraint represented by inequalities of the first degree.
  • Various algorithms have already been devised for the linear programming.
  • the linear programming is implemented using conditions of constraint and the objective function. By changing the objective function, there is obtained a result corresponding to a target of the system while satisfying the conditions of constraint.
  • ⁇ p is an unknown value indicating the ratio of time occupied by SDMA group #p
  • X pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p
  • TP q is the channel capacity required by station #q
  • m is the number of SDMA groups
  • n is the number of stations.
  • + ⁇ m (9) takes a minimum value, there are obtained, while satisfying the requirements, ⁇ 1 , ⁇ 2 , . . . , ⁇ m for which the period of time used by the overall system takes the minimum value.
  • ⁇ 1 , ⁇ 2 , . . . , ⁇ m for which the period of time used by the overall system takes the minimum value.
  • ⁇ p is an unknown value indicating the ratio of time occupied by SDMA group #p for uplink transmission
  • ⁇ p is an unknown value indicating the ratio of time occupied by SDMA group #p for downlink transmission
  • X pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p for uplink transmission
  • Y pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p for downlink transmission
  • TPX q is the channel capacity required by a station for uplink transmission
  • TPY q is the channel capacity required by a station for downlink transmission
  • m is the number of SDMA groups
  • n is the number of stations.
  • the priority is categorized into two types, namely, a fixed quantity guarantee type (or real-time type such as voice, video, and streaming) and a relative guarantee type (or non-real-time type such as e-mail).
  • a fixed quantity guarantee type or real-time type such as voice, video, and streaming
  • a relative guarantee type or non-real-time type such as e-mail.
  • ⁇ p is an unknown value indicating the ratio of time occupied by SDMA group #p for uplink transmission
  • ⁇ p is an unknown value indicating the ratio of time occupied by SDMA group #p for downlink transmission
  • X pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p for uplink transmission (fixed quantity guarantee type)
  • Y pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p for downlink transmission (fixed quantity guarantee type)
  • X′ pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p for uplink transmission (relative guarantee type)
  • Y′ pq is a known value indicating the channel capacity of station #q belonging to SDMA group #p for downlink transmission (relative guarantee type)
  • TPX q is the channel capacity required by a station for uplink transmission
  • TPY q is the channel capacity required by a station for downlink transmission
  • m
  • the wireless resource can be allocated to the station of fixed quantity guarantee type with higher priority. Moreover, by adding a condition that an objective function
  • step S 308 the system produce an allocation schedule by conducting a scheduling operation according to information regarding the wireless resource allocation for the respective stations determined by the optimizer 206 - c , namely, the SDMA groups and the periods of time allocated to the respective SDMA groups.
  • the system controls the wireless unit 202 , the signal processing unit 203 , the modem controller 204 , and the packet controller 205 .
  • the result of wireless resource allocation represents the periods of time allocated to the respective SDMA groups. Therefore, it is only necessary to allocate time according to the ratio thus determined at an interval of time for the scheduling.
  • the actual scheduling order is not restricted.
  • An example of implementing the embodiment is HCCA in the standard of IEEE802.11e. According to HCCA, there is prescribed a protocol in which the access point controls operation of the stations in a centralized way by use of the polling control technique such that the access point and the stations perform wireless communication according to the scheduling of the access point.
  • FIG. 13 shows an example of wireless resource allocation according to the present invention (in a conceptual graph).
  • the abscissa represents time
  • a period of time from a to b is allocated to wireless resources.
  • the ordinate represents channel capacity, which varies between the SDMA groups.
  • FIG. 14 shows a graph drawn after wireless resource allocation according to the present invention, the graph showing a relationship between the distance between an access point and a station and a probability of a case in which the required channel capacity is not secured.
  • Method 1 uses the MIMO technique, the quality of service is not taken into consideration, and a period of time obtained by equally dividing the channel estimation interval of time, 10 milliseconds (ms) is allocated to each station.
  • Methods 2 and 3 and the method of the present invention adopt the MIMO-SDMA technique. Method 2 does not take the quality of service into consideration.
  • the simulation since the number of simultaneous connections of stations is two, three stations are classified into two groups including a group including two stations and a group including one station at random.
  • Time is equally allocated to the SDMA groups.
  • the quality of service is taken into consideration. From the SDMA groups, four groups are selected, the four groups being mutually different from each other. A judge step is conducted to determine whether or not the four groups include a group which secures the required channel capacity. However, time is equally allocated to the groups. In the method of the present invention, a judge step is conducted to determine whether or not conditions of restriction is satisfied, using the linear programming.
  • the graph of FIG. 14 shows a relationship between the distance between an access point and a station of fixed quantity guarantee type and a probability of a case in which the required channel capacity is not secured.
  • FIG. 15 shows in a graph a relationship between the distance between an access point and a station of relative guarantee type and the total channel capacity of stations of relative guarantee type. It is assumed that the system includes stations of relative guarantee type in addition to three stations of fixed quantity guarantee type. In this situation, expression (13) in which the total channel capacity of the stations of relative guarantee type takes a maximum value is used as the objective function. It is assumed that the distance between the access point and each station of fixed quantity guarantee type is 15 meters and the channel capacity required by the station is 24 bits per second (bps). Among the stations, two stations request downlink transmission and one station requests uplink transmission. It is also assumed in this situation that, due to reversibility of the propagation path, one and the same channel capacity can be obtained for the downlink transmission and the uplink transmission.
  • the channel capacity of the stations of relative guarantee type can be secured while satisfying the requirements of stations of the fixed quantity guarantee type.
  • the present invention is applicable to the wireless communication systems.
  • the present invention is most efficiently applied to operation in which communication is conducted by allocating wireless resources using the SDMA technique.

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